Auto-loading rifles generally employ the energy produced in firing a round to cycle a bolt (bolt carrier and bolt) and load the next round. This includes machine guns and semi-automatic rifles of many types.
One type of system for transferring energy to the bolt employs the gas pressure developed behind the bullet in the barrel upon discharge. This is know as a direct-gas operated system. A small lateral vent hole is provided in the barrel (usually at a forward location), and the momentary gas pressure is transmitted through the vent hole back to the bolt assembly to cycle it. In direct-gas-operated rifles (such as an M16 or M4 rifle) the gas pressure is transmitted via a tube that extends back to the bolt, which has a piston-like portion to which the gas imparts pressure. In others (such as an M14) the gas pressure enters a cylindrical chamber, where a piston connected via a rod transmits the force back to the bolt assembly. This may either push the bolt assembly so that the rod and bolt assembly initially move together, or the rod may “tap” the bolt assembly, providing an impulse to move the bolt assembly rearward in its cycle.
The degree of force generated by the gas pressure is desired to remain in a selected range. Inadequate pressure can cause the firearms to fail to fully cycle, thus failing to chamber a round. Excessive pressure can cause excessive wear, and may damage components, as well as causing unreliable performance. Therefore, the aperture used to admit gas to the gas block from the barrel is carefully sized based on engineering principles, as is the aperture that allows gas from the gas block to vent to atmosphere. Each of these affect operation.
In some firearms, several apertures of different sizes are provided, with a rotating plug having the different sized apertures, so that whichever aperture is positioned over the gas passage from the barrel will determine the amount of gas admitted to the gas block. This permits the use of ammunition with different characteristics, and can compensate for powder fouling that can occlude or reduce the effective diameter of an aperture, reducing its gas transmission capability. In other versions, the variable aperture principle is applied to the aperture that vents the gases from the gas block, with a larger atmospheric vent aperture diminishing the pressure and duration in the gas block, for reduced action energy, and a smaller aperture maintaining and sustaining pressure at a higher level for increased action energy.
Other purposes of the selectable aperture diameter include the use of muzzle-mounted sound suppressors, which reduce the sound of the report generated upon firing. These briefly capture the pressurized gases emitted from the muzzle upon firing, so that the impulse is absorbed and spread out. The resulting peak pressure reduction provides a drastically reduced report. Suppressors also have the effect of increasing “backpressure,” because the moderately high pressure gases temporarily stored serve to slow the rate at which barrel bore pressures decline after the bullet exits the muzzle. This means that there is more pressure, working for a longer duration on the gas system. Consequently, the gas system should generally be set to a smaller aperture when suppressors are used, to avoid the problems with an over-pressurized gas system.
While such gas system adjustments are satisfactory for use with suppressors, problems can occur when a user installs a suppressor, but forgets to set the gas plug to a smaller aperture. This can cause unwanted damage, or a failure of the firearm to properly perform (with potentially dire consequences in a combat or self-defense context.)
The present invention overcomes the limitations of the prior art by providing a gas-operated firearm having a barrel defining a bore with a gas block defining a chamber communicating with the bore via a gas passage. A gas regulation element has a first position and a second position, and serves to provide different gas flow characteristics in the different positions. The latch element gives the user audible or tactile feedback upon installation of an accessory device when the gas regulation element is a correct position suited to use of the accessory, and not when in the other position unsuited to accessory usage. The accessory may be a sound suppressor, and the latch may serve to secure the gas regulation element against position change. The latch may engage a circular array of elements on the rear face of the suppressor, and may have an angled cam face to provide ratcheting engagement for installation, and to resist removal or loosening without deliberate actuation of the latch.